1. Field of the Invention
The present invention relates generally to solder masks for use on carrier substrates and, more particularly, to solder masks that are configured to prevent excess adhesive material from contacting or covering terminals of carrier substrates. In addition, the present invention relates to carrier substrates including such solder masks and to semiconductor device assemblies and packages including the carrier substrates. The present invention also relates to methods for designing solder masks to be used on carrier substrates, to methods for forming solder masks on carrier substrates, and to methods for connecting semiconductor devices to carrier substrates.
2. Background of Related Art
Circuit boards and other carrier substrates have long been employed to establish electrical communication between bond pads of semiconductor dice and other electronic components, including those carried by the circuit board and components that are external to the circuit board.
Conventionally, relatively small circuit boards have been used to package one or more semiconductor dice, which protects the dice and provides a semiconductor device package that includes a standardized connection pattern, regardless of the arrangement of bond pads of each semiconductor die of such a package. These circuit boards are often referred to in the art as xe2x80x9cinterposers.xe2x80x9d In the state of the art, the dimensions of interposers are approaching the corresponding dimensions of the semiconductor dice to be secured thereto, with the result being a continuous decrease in the sizes of semiconductor device packages, many of which are so-called xe2x80x9cchip-scale packagesxe2x80x9d exhibiting dimensions that are the same as or only slightly larger than those of the die thereof.
Nonetheless, when conventional wire bonding processes are used to electrically connect bond pads of a semiconductor die to corresponding contacts, or terminals, of an interposer to which the semiconductor die is back bonded, the terminals of the interposer must be positioned outside of the outer periphery of the semiconductor die. This requirement prevents a reduction in the size of these interposers to dimensions that are substantially the same as those of the semiconductor die to be secured thereto and carried thereby.
Moreover, in order to securely attach a semiconductor die to the circuit board, it is typically desirable that a sufficient amount of adhesive material be used to form a confluent adhesive layer adjacent to the back side of the semiconductor die and a fillet around the entire outer periphery of the semiconductor die. Some excess adhesive material is typically required to adhere the semiconductor die and the circuit board to one another in this manner. When excess adhesive material is used, however, some of the adhesive material may flow outward from the semiconductor die, beyond the desired location for a fillet, and contaminate the connection surfaces of adjacent terminals, which are located at the same elevation as or just above a surface of the circuit board. If the connection surfaces of the terminals become contaminated in this manner, intermediate conductive elements, such as bond wires, may not adhere thereto or form an effective electrical connection, which may ultimately reduce the reliability of the packaged semiconductor device, or cause electrical shorting and failure of the packaged semiconductor device.
Larger circuit boards, such as so-called xe2x80x9cmotherboardsxe2x80x9d and the substrates of so-called xe2x80x9cplug-and-playxe2x80x9d devices or cards, may be configured to carry a plurality of semiconductor devices. As with interposers, the trend with such larger circuit boards is also toward ever-decreasing sizes and ever-increasing densities. Consequently, contamination of the connection surfaces of terminals by adhesive material is increasingly encountered when semiconductor devices are assembled with larger circuit boards.
Solder masks are often used on circuit boards to facilitate the formation of solder balls or bumps on selected terminals of the circuit boards while protecting other features thereof and preventing solder from wetting and adhering to other features of the circuit board. The solder masks that are used on circuit boards are typically fabricated from photoresists, using known photolithography processes. These solder masks may be left in place while semiconductor devices and other components are secured and electrically connected to the circuit board. Thus, a semiconductor device may be secured to a solder mask which is, in turn, secured to the circuit board to which the semiconductor device is to be electrically connected.
When conventional solder masks are used on conventional circuit boards, a portion of the adhesive material that secures a semiconductor device to the solder mask may still flow laterally outward, beyond the outer periphery of the semiconductor device and onto connection surfaces of the adjacent terminals of the circuit board.
Some solder masks have been configured with recesses to receive some of the excess adhesive material. Nonetheless, these recesses typically do not have great enough volumes to contain all of the excess adhesive material that is forced from beneath a semiconductor device as the semiconductor device is secured to the solder mask and, thus, to the circuit board. Consequently, the terminals of circuit boards are typically spaced a sufficient distance away from the location at which the outer periphery of a semiconductor device to be secured to the circuit board is to be positioned that the connection surfaces thereof will not be contaminated by adhesive material. Such positioning of the terminals undesirably requires that the circuit board include additional real estate, which prevents a reduction in the dimensions of the circuit board.
The inventors are not aware of any carrier substrates or solder masks therefor that are configured to prevent adhesive material from flowing onto the connection surfaces of the carrier substrate terminals while reducing the dimensions of the carrier substrate.
The present invention includes a solder mask for use on a carrier substrate, such as a circuit board. The solder mask is configured to receive adhesive and prevent the same from contacting or otherwise covering connection surfaces of the terminals of the circuit board or other carrier substrate.
A solder mask according to the present invention includes semiconductor device-securing regions and may include recesses adjacent to the device-securing regions and which are configured to receive adhesive material, dams that are configured to laterally surround terminals of the circuit board, or a combination thereof. If the solder mask includes one or more recesses, or recessed areas, each recess may extend partially through the solder mask or completely therethrough. The collective volume defined between the outer periphery of a semiconductor device positioned upon a particular device-securing region of the solder mask and the solder dams and/or recesses that are adjacent thereto may receive substantially all of the excess adhesive material that is used to secure the semiconductor device to that supporting region. Accordingly, the height at which the supporting region positions a semiconductor device, as well as the depths and lateral dimensions of the recesses, may be configured to provide a volume that will receive excess adhesive.
In addition, one or more of the solder dams of the solder mask may extend laterally over a peripheral portion of the connection surface of the terminal around which it is positioned. The laterally extending regions of each such solder dam may also provide additional surface area over which adhesive material may spread before spilling over onto the corresponding terminal of the circuit board.
A circuit board upon which the solder mask is configured to be disposed may include terminals that protrude from, or are raised or elevated relative to, a surface thereof, increasing the volume within which adhesive material may be received. The distance the terminals protrude from the surface of the circuit board may provide a particular, desired volume between their corresponding solder dams and the location at which the outer periphery of a semiconductor device secured over the circuit board will be positioned. As an increased volume of adhesive material may be received between raised terminals and the location at which the outer periphery of a semiconductor device will be positioned, the terminals may be placed closer to their corresponding die-attach location than the terminals of conventional circuit boards and interposers. In addition, the connection surfaces of the terminals may be located at an elevation that is closer to the elevation at which the bond pads or other contacts of a semiconductor device are positioned over the circuit board. As a result of one or both of the closer spacing and raised elevation of the raised terminals, the raised terminals of a circuit board that incorporates teachings of the present invention may facilitate the use of shorter intermediate conductive elements between bond pads or other contacts of a semiconductor device and their corresponding terminals of the circuit board.
As used herein, the term xe2x80x9ccircuit boardxe2x80x9d is not limited to particular structures such as conventional FR-4 resin boards but encompasses any conductor-carrying, substantially planar substrate or other die support member formed of any suitable material, including without limitation conductor-carrying laminates formed of various materials, silicon or glass substrates with deposited (as by photolithography) conductors, ceramic substrates and other suitable conductor carriers as known in the art. Further, the term xe2x80x9ccircuit boardxe2x80x9d includes and encompasses all types of single-die and multi-dice assemblies, such as multi-chip modules (MCMs) including different types of dice or the same die type, the latter being exemplified by single in-line memory modules (SIMMs) or dual in-line memory modules (DIMMs).
Known techniques, including the use of adhesive material and positioning one or more semiconductor devices over the circuit board and in contact with the adhesive material, may be used to secure a semiconductor device to a circuit board carrying a solder mask according to the present invention. Upon being brought into contact with the adhesive material, positive pressure exerted by the positioning device and/or gravity may cause adhesive material between a support region of the solder mask on the circuit board and the semiconductor device to flow laterally outward, beyond an outer periphery of the support region and/or the semiconductor device. A receptacle formed at least in part by the solder mask will receive adhesive that is forced outward during placement of the semiconductor device. The volume of each adhesive receptacle, as well as the heights of the solder dams of the solder mask that laterally surround corresponding terminals of the circuit board, prevent adhesive material from contaminating the terminals.
A semiconductor device assembly incorporating teachings of the present invention includes a circuit board with the solder mask thereon, as well as at least one semiconductor device positioned over and secured to a corresponding support region of the solder mask. Contacts of the semiconductor device may be electrically connected to corresponding terminals of the circuit board by way of intermediate conductive elements, such as leads, bond wires, and conductive tape-automated bond (TAB) elements carried by a dielectric film. The semiconductor device assembly may also be partially or fully encapsulated.
The present invention also includes methods for designing circuit boards and solder masks to be used on circuit boards. The circuit boards, solder masks, or combinations thereof are configured to prevent excess adhesive material from contaminating the connection surfaces of circuit board terminals, while facilitating the placement of circuit board terminals more closely to the location at which the outer periphery of a semiconductor device will be located than the terminals of a conventional circuit board may be placed relative to the location at which the outer periphery of a semiconductor device thereon will be located.
A method for designing a solder mask in accordance with the present invention includes configuring at least one device-securing region and at least one corresponding recess or a plurality of dams laterally adjacent thereto. Alternatively, a combination of dams and recesses may be configured, with the dams being located adjacent to at least one recess, opposite from the corresponding device-securing region. The heights of the at least one device-securing region and the solder dams that correspond thereto, as well as the depth and lateral dimensions of the at least one corresponding recess, may be configured to provide a desired adhesive receptacle volume.
Additionally, the present invention includes a method for designing a circuit board to minimize contamination of the terminals thereof by excess adhesive. Such a method includes configuring terminals of the circuit board to protrude from a surface of the circuit board a distance that will provide a desired adhesive receptacle volume laterally between the terminals and a corresponding semiconductor device once the semiconductor device has been secured to the circuit board, while facilitating the connection of intermediate conductive elements to the terminals after the semiconductor device has been secured to the circuit board.
Other features and advantages of the present invention will become apparent to those of ordinary skill in the art through consideration of the ensuing description, the accompanying drawings, and the appended claims.